Through the Freedom of Navigation Program, established in 1979, the United States exercises diplomatic and military options for disputing maritime claims it judges to be inconsistent with customary international law and the United Nations Convention on the Law of the Sea. Yet, despite the United States’ universal commitment to freedom of navigation and the law of the sea, it has behaved inconsistently from 1979-2013. This dissertation examines the variation and asks under what conditions the United States demonstrates its refusal to acquiesce to maritime claims—either by issuing a diplomatic protest or driving a warship through the disputed waters. This dissertation introduces a new dataset of every coastal state in the world over this 34-year period, coding each type of maritime claim made by every coastal state in the world, whether the United States disputes that particular claim, and whether the United States takes some kind of diplomatic or operational action to dispute it. The mixed-method analysis proceeds with a large-n quantitative analysis that sets up a qualitative case study on the Strait of Hormuz. The dissertation begins and concludes with a discussion of current conditions in the South China Sea and the United States activity in this disputed region. This study finds that territorial and usage claims are twice as strongly correlated with operational assertions as a response than diplomatic protests. More specifically, coastal states that require foreign ships to obtain permission prior to entering their territorial sea are most highly correlated with operational assertions. When the United States disputes a maritime claim, military powers and wealthy states are no more likely to receive Freedom of Navigation operations (FONOPS) than others. Moreover, bilateral trade relationships and polity type hardly seem to matter. Similarly, neither the number of ships nor diplomatic representation increases the likelihood of FONOPS. Rather, a coastal state’s possession of nuclear weapons significantly increases the likelihood of receiving an operational assertion—especially if that states has made a declaration upon ratification of UNCLOS.